The present invention relates generally to optical elements, and liquid crystal display (LCD) devices using same.
LCD devices are widely used in personal communications equipment including, for example, mobile phone, personal computer and electric home appliance. In order to light a LCD, a back lighting and a front lighting are known. The back lighting surpasses the front lighting in providing good outward appearance at the display. A need remains for advanced technology toward enhanced brightness of back lighting. In order to enhance the brightness, there are several proposals. First, it is proposed to use light sources of increased brightness. Second, it is proposed to use optical films or the like. Third, it is proposed to use a light guide of increased brightness. Some of these proposals are as follows:
JP02-241590A discloses a light emitting panel assembly including a light guide. The light guide has a first surface, a second surface opposite to the first surface and a print pattern of white shapes formed on the first surface. The white shapes may be varied in the percentage and/or size in different areas of the light guide in order to provide a uniform light output distribution. Ordinarily, the amount of light traveling through the light guide is greater in areas closer to a light source than in other areas further remote from the light source. The pattern is used to adjust for the light variance by providing a denser concentration of white shapes with increased distance from the light source thereby resulting in a more uniform light output distribution from the light guide.
JP06-265731A discloses a light emitting panel assembly including a light guide. The light guide has a first surface, a second surface opposite to the first surface and a pattern of shallow circular depressions. The shallow circular depressions may be varied in diameter and/or depth in different areas of the light guide. The pattern is used to adjust for the variance of amount of light traveling through the light guide in different areas by providing a greater volume of shallow circular depressions with increased distance from a light source thereby resulting in a more uniform light output distribution from the light guide.
JP10-268138A discloses a light emitting panel assembly including a light guide. The light guide has a first surface and a second surface opposite to the first surface. A film including an array of prisms is attached to the first surface and another array of prisms is formed in the second surface.
Light extracting deformities, for example, dots, prisms, part-spheres, columns, square pillars, cones, or pyramids are produced by providing a molded pattern on the back surfaces of the light guides. Providing the molded pattern will require a permanent modification of a metal mold during adjustment for reducing or eliminating light output non-uniformity. Thus, the molded pattern cannot reinstate the previous pattern. For example, dots may be patterned onto a metal mold directly or they may be patterned onto a metal mold by etching.
FIG. 10 is an illustration of dots 103 produced by providing a molded pattern, using a metal mold with dots patterned directly, on a back surface 102 opposite to a light output surface 101 of an optical element in the form of a light guide 100. Each dot 103 has a spherical shaped lens surface 103a intersecting the back surface 102 and a transition 104 between the spherical shaped lens surface 103a and the back surface 102. Due to warp during fabrication of the metal mold, the transition 104 inevitably includes discontinuous and irregular angular configuration from the spherical shaped lens surface angular orientation to the back surface angular orientation. As indicated by arrows in FIG. 10, the transition 104 scatters a portion of light rays impinging on the transition 104 from a desired viewing axis and therefore reduces on-axis brightness.
FIG. 11 is an illustration of dots 103 produced by providing a molded pattern, using a metal mold with dots patterned by etching, on a back surface 102 opposite to a light output surface 101 of an optical element in the form of a light guide 100. Each dot 103 has a spherical shaped lens surface intersecting the back surface 102 and a transition 104 between the spherical shaped lens surface 103a and the back surface 102. As etching cannot produce the surface of metal mold to a desired level of smoothness, the spherical shaped lens surface 103a and the transition 104 inevitably have discontinuous and irregular angular configuration entirely. As indicated by arrows in FIG. 11, the spherical shaped lens surface 103a and transition 104 scatter light rays impinging on the spherical shaped lens surface 103a and transition 104 from a desired viewing axis and therefore reduce on-axis brightness.
FIG. 12 is an illustration of dots 103 produced by providing an inked pattern, using a screen printing, on a back surface 102 opposite to a light output surface 101 of an optical element in the form of a light guide 100. Ink 105 for screen printing contains beads 106. As indicated by arrows in FIG. 12, the beads 106 scatter input light rays from a desired viewing axis and therefore reduce on-axis brightness.
Attempts to increase on-axis brightness by efficient utilization of light include molded and/or printed patterns of dots. However, these attempts have not proven entirely satisfactory.